1. Field of the Invention
The present invention relates to a fundus camera for observing a fundus of a subject's eye with near-infrared light or visible light.
2. Description of the Related Art
Fundus cameras for observing and photographing a subject's eye fundus are roughly classified into a mydriatic type fundus camera to be used by applying a mydriatic to a subject's eye, and a non-mydriatic type fundus camera to be used without applying a mydriatic to a subject's eye. The former type fundus camera is used mainly by ophthalmologists. Usually, when a subject's eye fundus is photographed using the former type fundus camera, a plurality of images of the fundus is taken not only by a color photographing technique but also by various techniques, such as a fluorescent photographing technique and a special filter photographing technique. The latter type fundus camera is used mainly by doctors for medical check-up or physicians. When a subject's eye fundus is photographed using the latter type fundus camera, single shot photographing is mainly performed.
However, in recent years, needs for non-mydriatic photographing have grown among ophthalmologists, because the application of a mydriatic to a subject's eye can be omitted. Japanese Patent Application Laid-Open No. 9-66030 discusses a dual-use type fundus camera developed to be able to be used for both mydriatic photographing and non-mydriatic photographing, which can photograph both a dilated eye and a non-dilated eye.
The dual-use type fundus camera is provided with an optical finder. In a case where this dual-use type fundus camera is used as a fundus camera of the mydriatic type, an examiner observes a subject's eye fundus with visible light via the optical finder. On the other hand, in a case where the dual-use type fundus camera is used as a fundus camera of the non-mydriatic type, an examiner observes a subject's eye fundus with near-infrared light. A mirror that folds light back to the optical finder retreats to the outside of the optical path. Thus, reflection light from a fundus image is introduced to an imaging unit, such as a charge-coupled device (CCD), so that a fundus image is displayed on a monitor.
Further, the dual-use type fundus camera is configured such that when a subject's eye fundus is photographed, a mirror for splitting an optical path into an observing optical system and a photographing optical system retreats to the outside of the optical path, and that a fundus image is introduced to the imaging unit.
On the other hand, Japanese Patent Application Laid-Open No. 2003-135402 discusses a fundus camera which is not of the dual-use type usable for both mydriatic photographing and non-mydriatic photographing but of the non-mydriatic photographing type. However, this fundus camera is configured to perform both observing and photographing of a subject's eye fundus using a single imaging unit and to have a unit for presenting an internal fixation target. An optical path from a subject's eye is split by an optical path splitting prism into an optical path to the imaging unit and another optical path to the internal fixation target. The optical path splitting prism has characteristics adapted to transmit a part of light having a wavelength of light of the internal fixation target and to reflect light having the other wavelengths.
The dual-use type fundus camera usable for both mydriatic photographing and non-mydriatic photographing, which is discussed in Japanese Patent Application Laid-Open No. 9-66030, requires two components, i.e., a moving-image imaging unit for observing a subject's eye fundus, and a still-image imaging unit for photographing the fundus. Accordingly, the dual-use type fundus camera discussed in Japanese Patent Application Laid-Open No. 9-66030 has problems in that the configuration of the fundus camera is complex, and that the size of the fundus camera is large. In addition, when performing non-mydriatic photographing of a subject's eye fundus, the fundus camera needs an internal fixation target for guiding a line of sight of a subject's eye and for making the subject's eye fixate thereon. That is, the fundus camera requires another additional optical system therefor.
The fundus camera discussed in Japanese Patent Application Laid-Open No. 2003-135402 is configured to use a single imaging unit for both observing and photographing a subject's eye fundus in order to miniaturize the body thereof. Thus, the fundus camera can project an internal fixation target onto a subject's eye. However, the fundus camera requires the optical path splitting prism for splitting the optical path from a subject's eye into an optical path to the imaging unit and another optical path to the internal fixation target. When photographing a subject's eye fundus with visible light, the optical path splitting prism transmits light of wavelengths within a range corresponding to the wavelength of light of the internal fixation target, among the wavelengths of reflection light from the fundus. Thus, not all light reflected from the fundus can be incident on the imaging unit. Consequently, a loss of the amount of light occurs. In addition, no optical finder is provided in the fundus camera. Accordingly, a subject's eye fundus cannot be observed by direct vision.